1. Field of the Invention
Field of the present invention relates to a semiconductor device including an oxide semiconductor.
In this specification, the semiconductor device refers to all the devices that operate by utilizing semiconductor characteristics. A transistor described in this specification is a semiconductor device, and an electrooptic device, a semiconductor circuit, and an electronic device including the transistor are all semiconductor devices.
2. Description of the Related Art
Transistors (thin film transistors and the like) which are used for many liquid crystal display devices and light-emitting display devices typified by flat panel displays have included a silicon semiconductor such as amorphous silicon or polycrystalline silicon and have been formed over glass substrates.
Attention has been directed to a technique by which, instead of such silicon semiconductors, metal oxides exhibiting semiconductor characteristics are used for transistors. Note that in this specification, a metal oxide exhibiting semiconductor characteristics is referred to as an oxide semiconductor.
Examples of the oxide semiconductor include tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like which are single-component metal oxides, and In—Ga—Zn—O-based oxide, which is a homologous compound. Patent Documents 1 and 2 have already disclosed techniques in which such an oxide semiconductor is used to form transistors as switching elements and the like in pixels of a display device.
Semiconductor device using semiconductor characteristics of silicon include power devices for high power application in addition to the above-described liquid crystal display devices and light-emitting display devices. The power device is a semiconductor device which is indispensable to the power control of an electric device, and is used, for example, for a protective circuit of a battery of an electric device, or an inverter for driving an electric motor in a hybrid car.
For a typical power device, there are a rectifier diode, a power metal-oxide silicon field-effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), and the like; the power device needs favorable breakdown voltage characteristics and high output current.
For example, a technique in which silicon carbide (SiC) that is one of silicon semiconductors is used for a Schottky barrier diode which is superior in breakdown voltage characteristics is known (see Patent Document 3).